1. Field of the Invention
The present invention relates to a system and method for improving the system performance of a wireless communication network by controlling the dissemination of Routing packets, and decreasing the latency in finding routes between nodes. Specifically, the present invention provides a system and method of message exchanges to determine optimized communication routes with a minimum of overhead messages and buffered data.
2. Description of the Related Art
Wireless communication networks, such as mobile wireless telephone networks, have become increasingly prevalent over the past decade. These wireless communications networks are commonly referred to as “cellular networks”, because the network infrastructure is arranged to divide the service area into a plurality of regions called “cells”. A terrestrial cellular network includes a plurality of interconnected base stations, or base nodes, that are distributed geographically at designated locations throughout the service area. Each base node includes one or more transceivers that are capable of transmitting and receiving electromagnetic signals, such as radio frequency (RF) communications signals, to and from mobile user nodes, such as wireless telephones, located within the coverage area. The communications signals include, for example, voice data that has been modulated according to a desired modulation technique and transmitted as data packets. As can be appreciated by one skilled in the art, network nodes transmit and receive data packet communications in a multiplexed format, such as time-division multiple access (TDMA) format, code-division multiple access (CDMA) format, or frequency-division multiple access (FDMA) format, which enables a single transceiver at a first node to communicate simultaneously with several other nodes in its coverage area.
In recent years, a type of mobile communications network known as an “ad-hoc” network has been developed. In this type of network, each mobile node is capable of operating as a base station or router for the other mobile nodes, thus eliminating the need for a fixed infrastructure of base stations. Details of an ad-hoc network are set forth in U.S. Pat. No. 5,943,322 to Mayor, the entire content of which is incorporated herein by reference.
More sophisticated ad-hoc networks are also being developed which, in addition to enabling mobile nodes to communicate with each other as in a conventional ad-hoc network, further enable the mobile nodes to access a fixed network and thus communicate with other mobile nodes, such as those on the public switched telephone network (PSTN), and on other networks such as the Internet. Details of these advanced types of ad-hoc networks are described in U.S. patent application Ser. No. 09/897,790 entitled “Ad Hoc Peer-to-Peer Mobile Radio Access System Interfaced to the PSTN and Cellular Networks”, filed on Jun. 29, 2001, in U.S. patent application Ser. No. 09/815,157 entitled “Time Division Protocol for an Ad-Hoc, Peer-to-Peer Radio Network Having Coordinating Channel Access to Shared Parallel Data Channels with Separate Reservation Channel”, filed on Mar. 22, 2001, now U.S. Pat. No. 6,807,165, and in U.S. patent application Ser. No. 09/815,164 entitled “Prioritized-Routing for an Ad-Hoc, Peer-to-Peer, Mobile Radio Access System”, filed on Mar. 22, 2001, now U.S. Pat. No. 6,873,839, the entire content of each being incorporated herein by reference.
As can be appreciated by one skilled in the art, since certain nodes of the ad-hoc network are mobile, it is necessary for the network to maintain connectivity with those nodes. Transmitted data packets typically “hop” from mobile device to mobile device, creating a transmission path, or route, until reaching a final destination. However, transmission paths between mobile devices are often subject to change as devices move, therefore ad-hoc network communication must be able to adapt to achieve optimum performance while addressing the limited capabilities and capacities of mobile individual devices.
Wireless networks frequently use On-Demand protocols (e.g. ad-hoc on demand distance vector (AODV), (RFC 3561), dynamic source routing (DSR) (Internet Draft), and so forth, as the routing protocol in such communications. This type of routing protocol creates routes only when desired by the source node. When a node requires a route to a destination, it initiates a route discovery process within the network. This process is completed once a route is found or all possible route permutations have been examined. Once a route has been established, it is maintained by some form of route maintenance procedure until either the destination becomes inaccessible along every path from the source, or until the route is no longer desired.
Typically the Route Discovery involves broadcasting and forwarding Route Request (RREQ) packets until the route is found. All the application packets generated in the mean time are buffered at the source node. There can be a large latency associated with this route discovery if the destination is several hops away. This latency can be very large, particularly if an expanding ring search technique is used as is done in AODV. Transceivers typically used in these networks are memory constrained and hence a big latency can force them to drop packets from the buffer. The large latency can also be unsuitable for some applications especially the ones which use transmission control protocol (TCP).
The other drawback of the discovery process is the number of routing packets it generates/forwards during the process. These networks can span in large areas and such broadcasting and forwarding can tremendously increase the latency as well as the overhead. This overhead is even worse if the destination node does not even exist in the network, and in this case, the source node keeps repeating the discovery process and flooding the network in vain.
Accordingly, a need exists for a system and method to discover routes to a destination in an efficient way and also decrease the latency involved in finding the route.